Honey bee is a flying insect within genus Apis. There are seven main and 44 sub-species of honey bees out of which Apis mellifera has the main role in pollination and apiculture .
By Danyal Haider Khan, Raees Saleem, Shahid Iqbal ,Muhammad Awais Ahmad
Pollination in Sunflower:
Sunflower (Helianthus annuus) needs insects for pollination, a process in which pollen are transferred by vectors from male anther to female stigma for fertilization and seed production because sunflower is an allogamic plant due to morphological disagreement of stamen and pistal. Those plants that are cross pollinated are called allogamic plants.
Biology of Sunflower:
The H. annuus that is cultivated mostly have tall plants but with the development in science many varieties can have height between 50 to 500 cm. Sunflower seed is actually achene, monocarpellate (composed of single carpellate) and indehiscent (they donot open at maturity) . Yellow ray florets are present on the outer side and maroon or orange present on the inner side of each wider long capitulate of sunflower. Sunflower tilt during daytime towards the sun during growth phases but after the blooming starts they stop doing so.
Honey Bee role as pollinators:
Honey bee is a flying insect within genus Apis. There are seven main and 44 sub-species of honey bees out of which Apis mellifera has the main role in pollination and apiculture .Honey bees play a vital role in the pollination of sunflower cause they are excellent pollen collectors . Collection of pollens and nectar are essential as well as pollination and production of efficient seed with better genome.. Better genetic material means better yield and resistance against diseases and environmental hazards. Apis genera of honey bees have a strong impact on seed yield of sunflower genotype. Apis mellifera is one of the main species of honey bee. It is highly eusocial with single female queen and large colonies of infertile female workers, drones and larvae. Individual colonies can hold tens of thousands of individuals. There is a typical mechanism of complex communication between individual that including both use of pheromones and dance language.
Individuals (worker) can forge for nectar for a long distance and in various seasons and can carry heavy load during flight . Apis mellifera can help a large variety of plants in pollination due to its morphology and behavior. Role of A. mellifera varies through time and space in many studies it can be easily seen that mellifera have different role in different crops. Population of A. mellifera have been frequent visitor of flowering plants.
Apis mellifera behavior towards Sunflower:
The honey bee Apis mellifera visits sunflower at very high rate during the 2nd and 3rd day of flowering. The average density of A. mellifera during hyper activity is from 2.27 to 2.94 bees per capitulum (flower head). Bees that collect nectar are usually more frequent (2.28 bees per capitulum) than bees that collect pollen c (0.40 bees per capitulum). On the 3rd flowering day, mostly Helio 360 and Aguará hybrids have greater number of bee visits per flower head than the other genotypes. Seed yield is 43 % higher from sunflower plants that are visited by pollinator-insects compared with plants not visited by pollinators. Difficulties in the pollination of Sunflower by other factors
- There is morphological disagreement between stamen and pistal.
- Breeding system is not capable of self pollination.
- Pollens are not adaptable to anemophily ( wind pollination)
- Many insect unlike bees have less frequent visits to sunflower.
Seed formation in Sunflower:
From floral initiation to first stage of seed filling is the sensitive period that determines the number of seed in a floret this period many simultaneous processes takes place like root and stem development, leaf differentiation, floral differentiation, flowering etc. Disturbed growth following floret initiation causes empty achene. Lack of pollination causes defective fertilization that results in empty achene.Removal of florets or restricting of pollination can cause single mass achene . Seed yield mostly depend on the height and weight of capitulate of sunflower. Seed setting is sometimes heavily affected by wavelength of light other than pollination. Low seed setting means low yield that means low economic profit. Seed setting and seed filling are the major problems of sunflower that are both directly linked by the number of pollinators visiting the plant in a day.
Enhanced pollination in Sunflower:
Sunflower (Helianthus annuus L.) has important agronomic characteristics, such as resistance to drought, cold and heat. Sunflower cultivation is an important economic alternative in crop rotation and provides intercropping and succession of crops in seed-producing regions. The pollen of sunflower is too heavy and sticky to be carried by wind so honey bees play vital role in the pollination of sunflower. Sunflower is that specie in which pollen is viable during morning time so there are greater chances for honey bees to act as a vector for pollination. Even many nectar collecting bees are responsible for indirect pollination because they discard the pollen into pollen basket of other capitula. Actually sunflower pollen is less attractive for honey bees so sunflower develops excellent strategy by attracting honey bees by nectar that act as a vector for direct and indirect pollination.
It was observed in a research that average number of honey bees visiting per capitula per time was from 2.73 to 2.94 that was satisfactory for the excellent pollination for increasing the yield of the sunflower seed . It was also observed that during flowering time the average visitation of Apis mellifera was 5.84 per capitulum. It was also observed that honey bees show variation in the foraging behavior towards different genotypes of sunflower due to different reasons. The main reason for the variation in attractiveness of sunflowers genotype was due to difference in the sugar content of the nectar. When sucrose solution was applied to the capitulum it shows positive results. The other factors for showing variation in the attractiveness of pollen towards bees was the height and weight capitulum, sowing and flowering period of flower and seasonal variability.
In another research it was observed that more bees visited the hybrid Helio 360 and Aquara genotypes ase compared to the genotypes Helio 251 , Charrua and Multissol . This difference may be caused by the difference in attraction of genotypes. The main reason for this difference might be the different concentration of sucrose secreted and the availability of nectar and pollen throughout the day .
Although there is variation among the foraging behavior of honey bees towards different genotypes of sunflower that have different height and weight of capitulum. Seed set was different in different genotypes due to difference in attractiveness of plants towards bees that clearly reflects in the seed setting of the plants depending on their genotypes. By identifying the differences in attractiveness to bees (pollinators ) to the hybrid genotype of sunflowers can be detrimental in increasing the yield of plant species that are depending on the biological agents (pollinators ) for their reproduction , in addition to providing support to the plant breeders in genetic selection of more productive varieties that have more attractive nectar that have optimum quantity of sucrose and the right position of pollen. Different researches have shown different results the most precise of them shows 63% increase in seed setting and 43 % higher yield compared to the plants that were restricted to the pollinators. found out that African bees increase seed setting by 38% or 53% in some areas respectively.
Sunflower Pollination in Pakistan:
Sunflower is mostly sown two weeks after the last spring frost . It is one of the the four main annual crops harvested for oil seed in the world. In Pakistan it was introduced as oil seed crop 40 years ago. But it production in acreage has been fluctuating due to various reasons like socio-economic factors. Its seed contains 35-55% oil contents. Many research work has shown that this crop has great potential under Pakistani agricultural climatic conditions in rainfed and irrigated areas in different agro-ecological zones.
The suitable area for this crop is cotton growing belt ( Vehari , Lodhran , Bahawalpur , Umerkot) and rice growing belt of upper Punjab and Lower Sindh. The crop is grown in spring as well as in autumn that gives average yield of 1.3 tons per hectare. It is highly suitable to keep a bee hive in every plot and using bee attractant genotypes. It has good prospects as intercrop with sugarcane, if suitable hybrids and production technology is available. During 2000-01, the area was 58998 ha and increased to 319743 ha in 2008-09 with production of 420487 tons and per hectare yield of 1315 kg. This crop and is successfully grown under different climatic conditions of the country, i.e., in the warm and harsh conditions of southern part of the country to mild and cool climate in the north. It has great potential to bridge the gaps between the production and consumption.
Author: Danyal Haider Khan, Raees Saleem, Shahid Iqbal ,Muhammad Awais Ahmad, Institute of Plant protection, MNS University of Agriculture, Multan